Motor control for a treadmill having improved power supply and improved speed regulation under intermittent loading

Abstract

A motor control for a treadmill has an improved, inexpensive, and simple set of power supplies, derived from the bus voltages of the DC busses with simple voltage dividers, to supply operational amplifiers connected to the positive DC voltage bus with a dual voltage supply and a common or neutral, and to provide a single voltage power supply connected to the negative bus for the driving circuitry of a motor energization switching controlling element. The dual power supply for the operational amplifiers comprises a voltage divider containing two, series connected zener diodes in series with a resistor. The one of the series connected zener diodes is connected to the positive DC voltage bus, and the resistor is connected to the negative DC voltage bus. A common connection between the two zener diodes becomes the neutral or common voltage for the operational amplifiers, and the zener diode voltages become the positive and negative supply voltages for the amplifiers. The power supply for the driving circuitry of the switch element is structured with a voltage divider comprising one zener diode and a series connected resistor. In this case, the zener diode is connected to the negative bus and the resistor to the positive bus. Isolation between the two power supplies is accomplished with optical, capacitive, or transformer isolation. The regulating circuit of the motor control may include circuitry for compensation for the inductance voltage drop in the armature circuit of the motor.

It is claimed: 
     
       1. A drive for energizing a DC motor driving a treadmill, said drive comprising: a DC power supply having a positive polarity voltage bus and a negative polarity voltage bus, said buses being connectable to the treadmill drive motor;   switching means in one of said buses for being connected in series with said DC motor for energizing the DC motor from said DC power supply to provide variable voltage to the DC motor;   regulating means for controlling the operation of the DC motor, said regulating means including driving means for driving said switching means and amplifier means for controlling said driving means, said amplifier means being connected to one of said positive and negative polarity voltage buses, and said driving means connected to the other said positive and negative voltage buses;   a dual polarity power supply for powering said amplifier means, said dual polarity power supply comprising first and second zener diodes connected in series, said series connected zener diodes being further connected in series with a first resistor, each of said zener diodes having a preselected voltage drop thereacross, said first zener diode having a first terminal connected directly to said one of said voltage buses, said first zener diode having a second terminal connected to a first terminal of said second zener diode, the connection of said second terminal of said first zener diode and said first terminal of said second zener diode comprising a common connection between said zener diodes, said second zener diode having a second terminal connected to a first terminal of said first resistor, a second terminal of said first resistor being connected to said other voltage bus, the zener voltage drops across said first and second zener diodes providing positive and negative constant magnitude voltages with respect to the common connection between said first and second zener diodes, the magnitude of said positive and negative constant magnitude voltages being that of the preselected zener voltage drops, the common connection and both said positive and negative constant magnitude voltages being provided to said amplifier means as operating voltages for powering said amplifier means; and   a power supply for powering said driving means, said power supply comprising a third zener diode, said third zener diode having a first terminal connected directly to said other voltage bus, and a second terminal connected to a first terminal of a second resistor, a second terminal of said second resistor being connected to said one of said voltage buses, said third zener diode having a preselected voltage drop thereacross providing a constant magnitude voltage which is provided to said driving means as an operating voltage for said driving means.   
     
     
       2. The drive according to claim 1 further including isolation means between said amplifier means and said driver means. 
     
     
       3. The drive according to claim 2 wherein said isolation means comprises opto-isolation means. 
     
     
       4. The drive according to claim 2 wherein said isolation means comprises transformer isolation means. 
     
     
       5. The drive according to claim 2 wherein said isolation means comprises capacitive isolation means. 
     
     
       6. The drive according to claim 1, wherein said regulating means provides an output signal controlling the armature voltage applied to the motor, and wherein said drive comprises: means for providing a speed reference signal corresponding to the desired speed of said motor to said regulating means;   means for providing an armature voltage feedback signal to said regulating means, said armature voltage feedback signal being supplied in opposition to said speed reference signal to produce an error signal for operating said regulating means to establish the armature voltage, and hence the speed of said motor;   means for sensing the armature current of the motor;   means coupled to said armature current sensing means for providing an IR compensating signal to said regulating means to compensate for the voltage drop resulting from the resistance of the armature circuit, said signal being provided in a manner that is additive to said speed reference signal for altering the output of said regulating means in a manner tending to establish the speed of said motor at that corresponding to said speed reference signal; and   means coupled to said armature current sensing means for obtaining a signal corresponding to the additional voltage drop resulting from the inductance of the armature circuit when the motor is subjected to transient load changes and for providing said signal to said regulating means in a manner that is additive to said speed reference signal for altering the output of said regulating means in a manner tending to establish the speed of said motor during the transient load changes at that corresponding to said speed reference signal.   
     
     
       7. The drive according to claim 6 wherein said inductance voltage drop obtaining means comprises a capacitor subjected to a voltage proportional to the armature current. 
     
     
       8. The drive according to claim 7 further including a noise limiting resistor in series with said capacitor. 
     
     
       9. The drive according to claim 6 wherein said inductance voltage drop signal obtaining means includes an inductor subjected to the armature current. 
     
     
       10. The drive according to claim 1 wherein said regulating means provides an output signal controlling the armature voltage applied to the motor, and wherein said drive comprises: means for providing a speed reference signal corresponding to the desired speed of said motor to said regulating means;   means for providing a speed feedback signal to said regulating means, said speed feedback signal being supplied in opposition to said speed reference signal to produce an error signal for operating said regulating means to establish the armature voltage and hence the speed of said motor;   means for sensing the armature current of the motor; and   means coupled to said armature current sensing means for obtaining a signal corresponding to the voltage drop resulting from the inductance of the armature circuit when the motor is subjected to transient load changes and for providing said signal to said regulating means in a manner tending to establish the speed of said motor during the transient load changes at that corresponding to said speed reference signal.   
     
     
       11. The drive according to claim 10 wherein said inductance voltage drop signal obtaining means comprises a capacitor subjected to a voltage proportional to the armature current. 
     
     
       12. The drive according to claim 11 further including a noise limiting resistor in series with said capacitor. 
     
     
       13. The drive according to claim 10 wherein said inductance voltage drop signal obtaining means includes an inductor subjected to the armature current. 
     
     
       14. The drive according to claim 1 wherein said first terminal of said first zener diode is connected directly to said positive DC voltage bus, said second terminal of said first resistor is connected to said negative DC voltage bus, and said first terminal of said third zener diode is connected to said negative DC voltage bus and said second terminal of said second resistor is connected to said positive DC voltage bus. 
     
     
       15. The drive according to claim 1 wherein said first resistor and said second resistor are combined as a single resistor connected between said second terminal of said second zener diode and said second terminal of said third zener diode so that said first, second, and third zener diodes and said single resistor are connected in series across said voltage buses.